Tax1bp1 enhances bacterial virulence and promotes inflammatory responses during Mycobacterium tuberculosis infection of alveolar macrophages

Abstract

Crosstalk between autophagy, host cell death, and inflammatory host responses to bacterial pathogens enables effective innate immune responses that limit bacterial growth while minimizing coincidental host damage. Mycobacterium tuberculosis (Mtb) thwarts innate immune defense mechanisms in alveolar macrophages (AMs) during the initial stages of infection and in recruited bone marrow-derived cells during later stages of infection. However, how protective inflammatory responses are achieved during Mtb infection and the variation of the response in different macrophage subtypes remain obscure. Here, we show that the autophagy receptor Tax1bp1 plays a critical role in enhancing inflammatory cytokine production and increasing the susceptibility of mice to Mtb infection. Surprisingly, although Tax1bp1 restricts Mtb growth during infection of bone marrow-derived macrophages (BMDMs) (Budzik et al. 2020) and terminates cytokine production in response to cytokine stimulation or viral infection, Tax1bp1 instead promotes Mtb growth in AMs, neutrophils, and a subset of recruited monocyte-derived cells from the bone marrow. Tax1bp1 also leads to increases in bacterial growth and inflammatory responses during infection of mice with Listeria monocytogenes, an intracellular pathogen that is not effectively targeted to canonical autophagy. In Mtb-infected AMs but not BMDMs, Tax1bp1 enhances necrotic-like cell death early after infection, reprogramming the mode of host cell death to favor Mtb replication in AMs. Tax1bp1s impact on host cell death is a mechanism that explains Tax1bp1s cell type-specific role in the control of Mtb growth. Similar to Tax1bp1-deficiency in AMs, the expression of phosphosite-deficient Tax1bp1 restricts Mtb growth. Together, these results show that Tax1bp1 plays a crucial role in linking the regulation of autophagy, cell death, and pro-inflammatory host responses and enhancing susceptibility to bacterial infection. Author SummaryAlthough macrophages are the first innate immune cells to encounter Mycobacterium tuberculosis during infection, M. tuberculosis has evolved the ability to persist in them. Recent studies highlight that some types of macrophages are more permissive to M. tuberculosis replication and survival than others, but the mechanisms for cell type-specific differences in M. tuberculosis growth are only beginning to be understood. We found that the host factor, Tax1bp1 (Tax-1 binding protein 1), supports M. tuberculosis growth during animal infection and in specific subsets of innate immune cells, including alveolar macrophages while restricting M. tuberculosis in bone marrow-derived macrophages. We also found that Tax1bp1 has a similar phenotype in enhancing the pathogenesis of another intracellular pathogen, Listeria monocytogenes. Compared to bone marrow-derived macrophages, in alveolar macrophages, Tax1bp1 enhances the release of inflammatory mediators and leads to necrotic-like host cell death, which is known to enhance M. tuberculosis growth. Phosphorylation of Tax1bp1 in alveolar macrophages promotes M. tuberculosis growth. Our research highlights that Tax1bp1 is a host target for host-directed therapy against M. tuberculosis and controls host responses to M. tuberculosis in a cell type-specific manner.